xx THE CHURCH OF THE GASTRIA 271 within and showing five sides on the exterior, is attached to the eastern arm. Its three central sides are occupied by a triple-shafted window. Two shallow niches represent the usual apsidal chambers. A similar niche is found also on both sides of the entrance and on the eastern side of the northern arm of the cross. In the wall to the west of the southern arch is a small chamber. The joint between the apse and the body of the building is straightj with no bond in the masonry ; nor is the masonry of the two parts of the same character. In the former it is in alternate courses of brick and stone3 while in the latter we find many brick courses and only an occasional stone band. Evidently the apse is a later addition. In view of these factSj the probable conclusion is that the building was originally not a church but a library 3 and that it was transformed into a church at some subsequent period in its history to meet some special demand.